1. Field of the Invention
The invention relates to heat-formed composite panels comprising at least two bonded fiber-based layers which are used in particular as a heat screen for the insulation of motor or other automobile components.
2. Background of the Prior Art
Composite panels based on mineral fibers of the glass fiber type bonded with a heat-hardenable organic resin are, for example, used as baffles, hood liners or interior flare opening liners in automobiles. They are manufactured by heat-forming a rough component composed of one or several layers of fibers impregnated with a binder which is at most partially polymerized, coated at least on one of its surfaces with a facing, for example in cloth. Such panels, of variable thickness, are rigid and have good mechanical holding. However, the risk of degradation of the organic binder through heat decomposition prevents their use near parts continuously exposed to more than 300.degree. C. Consequently, such composite panels do not satisfy the requirements for a heat screen protecting, for example, a turbocompressor, which operates for automobiles at slightly more than 700.degree. C., a catalytic muffler where maximum efficiency is obtained with gases at approximately 700.degree. C. or even for the covering from beneath of the motor with a view to better penetration in the air of the vehicle.
However, numerous fibers can take such temperatures. For example, basaltic rock or slag fibers, silico-aluminous fibers (ceramic fibers), asbestos fibers, etc., can be mentioned. Glass fibers also resist with no problems at temperatures around 450.degree. C. The difficulty is to find a satisfactory binder. Therefore, for such temperatures, a mineral binder of the clay type, such as an alkaline silicate, an ethyl silicate, an alumina phosphate or even colloidal alumina must most often be used. These binders are efficient up to 700.degree.-1200.degree. C. but, unfortunately, the formed products obtained are fairly friable and are suitable only for static uses and not in locations which are frequently under vibration, such as automobiles.